For a dam long time or at least until you've strained so much that aditional shooting is almost impossible.

I know that is criptic but last year I screwed up. I had deer all evening long come by and there was a ten point I debated on shooting for about ten minutes. He was about 135-140. He was nice but I knew I wouldn't get him mounted. I decided it was still early in the evening and I could shoot him and still have a chance at one of the huge deer that we were seeing everytime out if he came by. Well to make a long story longer, I drew on him as he went behind a tree. One of the other deer around must have caught my movement or sensed something because they all frooze for about 5 mins. I held as long as I could before I had to let it back down. He came around and gave me another shot and I got one off. It hit a twig about 4' in front of him and nose dived to the ground. He ran off but oh well. 20 mins later a huge 8 point came up and I was too worn out to draw back. I watched him walk 10 yrds broadside.

Moral of the story is to have patience and wait for the one you want don't get greedy and don't hold your bow for too long at full draw.

Good luck